1. Field of the Invention
This invention relates generally to mud pumps for use in water well drilling operations, and more particularly to a motor driven centrifugal-type mud pump assembly having a close-coupled direct drive hydraulic motor and a case-drain-pressurized pump shaft seal assembly at the mud pump impeller end of the shaft.
2. Description of the Prior Art
During water well drilling operations, it is usually necessary to pump muddy water. Though some pumps are of a reciprocating type, most pumps used for this purpose are rotary pumps, primarily because they are much less expensive than reciprocating pumps. One problem that is very common with rotary pumps is seal failure due to the abrasives in the mud being pumped.
Many mud pumps are driven by a hydraulic motor through a coupling shaft assembly such that the motor is spaced sufficiently from the pump for access to a pump shaft seal packing housing to facilitate replacement of seals. Depending upon the manner and environment of use of the pump, seal failures can occur as often as daily, resulting in significant down-time during replacement of a seal assembly. In addition, due to the necessity of having enough space to change a seal, the pump and drive motor assembly has an overall length that is objectionable.
Since the pump impeller has a high rotational speed, and must be supported in the housing by suitable bearings, leakage of muddy water into the bearing area is intolerable. At one time, asbestos was used as a component of pump shaft seal packing. Health and environmental concerns have since dictated the exclusion of asbestos from such materials, resulting in a reduction in the packing life.
As is true of many mechanical devices, provisions are typically made for greasing pump bearings by using a grease gun. But this requires regular attention by an operator to be certain that greasing is done on a timely and adequate basis. Also, it is important to avoid excessive pressure such as could cause the blow-out of a shaft seal.
It is an object of the present invention to provide a mud pump shaft sealing system facilitating close coupling of the pump and drive motor, and providing comparatively long seal life.